Field of the Invention
Embodiments of the invention relates to a boiler of a circulating fluidized bed, in particular to a furnace of a large size circulating fluidized bed boiler.
Description of the Related Art
Large-sizes and high-parameters are the inevitable trend of technological development of boilers for circulating fluidized beds. As a capacity of a boiler and an area of a cross section of a furnace increase, it is difficult for a secondary air to reach the center of the furnace; and at the same time, As parameters of boiler steam raise, especially when the parameter are raised to supercritical or ultra-supercritical steam parameters, heat releasing volume of a furnace increases faster than a heating surface of the furnace does, thus, an unbalanced growth between heat releasing and heat absorption leads to a problem concerning the arrangement of the heat plate. Therefore, passage of the secondary air and arrangement of the heat plate have become main bottlenecks that constraint the trend of technological development of circulating fluidized bed boilers toward large-sizes and high-parameters.
To solve the problem of passage of secondary air, Chinese Patent ZL 200710151813.0 discloses a furnace of a circulating fluidized bed boiler having a water-cooled column, the water-cooled column formed by membrane walls is disposed between an air distributing plate and a ceiling of the furnace to increase an area of the heat plate of the furnace, and secondary air is passed through the water-cooled column to the combustion chamber of the furnace. Since conducts for the secondary air should be arranged inside of the water-cooled column and require a certain space for arranging the conduits and maintenance, sizes of the cross section of the water-cooled column according to conventional designs will be relatively larger, which will lead to a small distance between an inner wall and an outer wall of the combustion chamber of the furnace having an annular shape, such that mixing of materials inside the furnace and arrangement of plate-typed heating plate will be adversely affected. In addition, generally, when only one conventional square water-cooled column is disposed inside the chamber, lower parts of four water-cooled sidewalls of the furnace are inclined inwardly, in order to provide a combustion space of the furnace having a cross section that increases gradually. In such a manner, the design and arrangement of the water-cooled sidewalls of the furnace are relatively complicated.